Add kqueue parent-death watcher for Python sidecars

[EtanHey]

Summary

• add a macOS/BSD kqueue NOTE_EXIT parent-death watcher for BrainLayer Python sidecars
• install it in BrainBar/MCP/daemon/watch/enrich/drain sidecar entry points
• add a real subprocess test that proves a child exits within 1s after its parent dies

Verification

• PYTHONPATH=src pytest tests/test_parent_death.py tests/test_brainbar_hybrid_helper.py tests/test_cli_enrich.py tests/test_jsonl_watcher.py tests/test_daemon_kg.py tests/test_mcp_input_schema_limits.py tests/test_lifecycle.py -q
• ruff check src/ tests/ brain-bar/Scripts/brainbar_stdio_adapter.py
• ruff format --check src/ tests/ brain-bar/Scripts/brainbar_stdio_adapter.py
• swift test --filter SocketIntegrationTests (from brain-bar/)

Notes

• The kqueue behavior is active only where Python exposes select.kqueue; other platforms no-op.
• BRAINLAYER_DISABLE_PARENT_DEATH_WATCH=1 disables the watcher for emergency/debug runs.
• Full local pytest collection is blocked by local environment deps: missing deepchecks and NumPy 2.4 incompatible with numba/ranx.

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Note

Medium Risk
Medium risk because it changes lifecycle/termination behavior for multiple persistent processes and uses a background kqueue thread with os._exit, which could surface platform-specific edge cases.

Overview
Adds a new brainlayer.parent_death.install_parent_death_watcher() implementation using BSD/macOS kqueue NOTE_EXIT to terminate Python sidecar processes when their parent exits (with an env var escape hatch and no-op behavior on unsupported platforms).

Installs the watcher at startup across several long-running entry points (daemon, MCP stdio server, drain loop, enrichment pipeline runner, hybrid helper, CLI enrich/watch, and BrainBar’s brainbar_stdio_adapter).

Introduces tests/test_parent_death.py, including a subprocess-based integration test that verifies the child process exits shortly after its parent terminates, plus a unit test for the no-kqueue fallback and a check that entrypoints include the watcher.

^{Reviewed by Cursor Bugbot for commit edf76d1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add kqueue parent-death watcher to Python sidecar processes

• Adds parent_death.py with install_parent_death_watcher(), which uses kqueue/EVFILT_PROC to monitor the parent PID and calls os._exit(0) in a daemon thread when the parent exits.
• Installs the watcher at startup in all long-running entrypoints: daemon, drain, MCP stdio server, CLI enrich and watch commands, hybrid helper, enrichment pipeline, and the stdio adapter.
• Can be disabled by setting BRAINLAYER_DISABLE_PARENT_DEATH_WATCH; no-ops silently on platforms without select.kqueue (i.e. non-BSD/macOS).
• Adds tests covering the no-kqueue no-op path, a live parent-death integration test, and a coverage check that all entrypoints call install_parent_death_watcher.

^{Macroscope summarized edf76d1.}

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 8e8a2b3a-ad94-4b5e-bd2a-c1d743b844b1

📥 Commits

Reviewing files that changed from the base of the PR and between 8bf7b75 and edf76d1.

📒 Files selected for processing (9)

• brain-bar/Scripts/brainbar_stdio_adapter.py
• src/brainlayer/brainbar_hybrid_helper.py
• src/brainlayer/cli/__init__.py
• src/brainlayer/daemon.py
• src/brainlayer/drain.py
• src/brainlayer/mcp/__init__.py
• src/brainlayer/parent_death.py
• src/brainlayer/pipeline/enrichment.py
• tests/test_parent_death.py

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/kqueue-pdeath

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[EtanHey]

@codex review
@cursor review
@BugBot review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

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